Subject: [rohc] Interpretation intervals for TS encoding

From: "Endre Szalai \(IJ/ETH\)" <[email-masked]>
Date: Tue, 23 May 2006 18:31:08 +0200

Hi ROHCers,

reading the "Corrections and Clarifications to RFC 3095"
(draft-ietf-rohc-rtp-impl-guide-19.txt) document, the last paragraph of
section 4.3 is not really clear for me.

"Since two different p-values are used, the compressor must take this
 into account throughout the process of enabling timer-based
 compression (see section 4.8 of this document). During transition
 from window-based compression to timer-based compression, it is thus
 necessary that the compressor keep k large enough to cover both
 interpretation intervals."

When the HC wants to use timer based compression, it will start sending
a positive TIME_STRIDE value (after of course a valid CLOCK option is
propagated from the HD). If the HD receives such a packet, it will
switch to timer based compression immediately. This means, that the HD
will use the value for "p" as specified in section 4.5.4 in RFC 3095)
when decompressing received TS bits (if any), and not the "p" value for
the W-LSB encoding.

Why and how the HC should consider the "p" value for W-LSB encoding in
this case ?

The HC keeps track of all possible references the HD may have, and the
HC will simply apply timer based compression with the proper "p" value.
Since HD will use the same "p" value (TIME_STRIDE > 0), how could the 2
different interpretation intervals interfere ?

Could someone give a clarification on this (maybe an example) ?

Thanks,
Endre

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